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Table 4 Quartile level of WBC DNA methylation and risk of breast cancer by date of DNA extraction, and by time between blood collection and diagnosis, stratified by DNA extraction method

From: White blood cell DNA methylation and risk of breast cancer in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO)

  Quartiles of DNA methylation
  Q4 (high) Q3 Q2 Q1 (low)
Period of DNA extraction
 Previously extracted DNA
  Adjusted ORa 1. 0 (referent) 0.99 1.01 1.44
  95% CI   (0.5–1.9) (0.5–2.0) (0.8–2.7)
  Cases, controls 33, 36 33, 36 34, 36 51, 39
 Newly extracted DNA
  Adjusted ORa 1.0 (referent) 0.84 0.82 0.61
  95% CI   (0.5–1.3) (0.5–1.3) (0.4–1.0)
  Cases, controls 81, 65 74, 70 68, 66 54, 71
Time from blood collection to diagnosis
 Previously extracted DNA
  1 to <2 years
   Adjusted ORa,b 1.0 (referent) 0.99 1.16 1.41
   95% CI   (0.4–2.7) (0.4–3.0) (0.6–3.6)
   Cases, controls 11, 36 10, 36 13, 36 16, 39
  2 to <4 years
   Adjusted ORa,b 1.0 (referent) 1.15 1.00 1.39
   95% CI   (0.5–2.7) (0.4–2.4) (0.6–3.2)
   Cases, controls 14, 36 16, 36 14, 36 21, 39
   ≥ 4 years
   Adjusted ORa,b 1.0 (referent) 0.89 0.97 1.53
   95% CI   (0.3–2.8) (0.3–3.1) (0.6–4.3)
   Cases, controls 8, 36 7, 36 7, 36 14, 39
 Newly extracted DNA
  2 to <4 years
   Adjusted ORa,b 1. 0 (referent) 0.88 0.73 0.68
   95% CI   (0.5–1.5) (0.4–1.3) (0.4–1.2)
   Cases, controls 43, 65 43, 70 32, 66 33, 71
  ≥4 years
   Adjusted ORa,b 1.0 (referent) 0.80 1.00 0.51
   95% CI   (0.4–1.5) (0.6–1.8) (0.3–1.0)
   Cases, controls 38, 65 31, 70 36, 66 21, 71
  1. aAdjusted for age and time at entry
  2. bSame controls are used for each category of elapsed time from blood collection to diagnosis, within period of DNA extraction (previously extracted, newly extracted); OR Odds Ratio